The game of golf requires that the players possess the skill of hand to eye coordination. In particular, a high degree of accuracy is required when putting the ball. The accuracy of a golfer's putt is primarily dependent upon three factors. First, the golfer must determine the correct line of travel of the ball to an intended target. This requires that the golfer set up an imaginary line from the ball to the hole, referred to as the correct line of the putt. Second, the golfer must ensure that the putter face is perpendicular to the correct line of the putt. If the putter face is not positioned in this manner, the ball will travel at an angle away from the hole. Consequently, even a slight twisting of a golf putter away from the proper position can result in a missed putt. This is particularly frustrating to the golfer who has a natural tendency to turn his wrists during the swing, or the golfer who has difficulty discerning a slight rotation away from perpendicularity. Finally, the golfer must strike the ball with the correct force to propel it to the hole.
Errors associated with any one of these three factors can result in a missed putt. However, the accuracy of a golfer's putt is particularly sensitive to very small changes in the angle of the putter face to the correct line of the putt. FIG. 1 shows that a golf ball travels perpendicular (at an angle of 90.degree.) to the position 34, 34' of the putter face when hit with a conventional flat putter face. Thus, to avoid missing the putt, the golfer must align the putter face 34 essentially perfectly perpendicular to the correct line of the putt 31. A slight rotation, .theta., of the putter face from position 34 to position 34' will direct the ball away from the hole in line of travel 35.
The table shown in FIG. 2 provides a comparison of the potential offset x of the ball from the hole when hit by a putter face which is not perpendicular to the correct line of the putt. An offset of greater than about 1.5 inches is considered a miss. The offsets created by changing the angle .theta. in half degree increments is shown in the table columns. Where .theta. is 1.5 degrees or more, the hole will be missed at a putt distance as close as 5 feet. Similarly, a review of the offsets at putt distances ranging from 5 to 30 feet shows that the effect of non-perpendicularity becomes more significant as putt distance is increased. For example, at a putt distance of 15 or more feet, a half degree rotation from perpendicularity creates enough offset to cause a missed putt. Similarly, if the variation in perpendicularity is 1.5 degrees or more, the hole will be missed at a putt distance as close as 5 feet.
Changes in the perpendicularity of the putter face to the correct line of the putt typically occur for two reasons. First, a golfer's stance during putting is generally such that his or her eye level is three to four feet above the ball. From this height, it is difficult to judge whether or not the putter face is perpendicular to the correct line of the putt. Moreover, the ability to discern a few degrees change from perpendicularity is difficult, if not impossible, for some golfers. Second, even if the golfer is able to align the putter face perpendicular to the correct line of the putt, non-perpendicularity often results due to movement of the golfer's wrists at the moment of impact in his or her swing.
Others have previously attempted to utilize curvature in the design of the driving face of the putter to compensate for variations in the angle of the putter face to the line of the putt. U.S. Pat. No. 3,989,257 to Barr discloses a putter which is directed to correcting the problem of slight wrist movements on the part of the golfer at the moment the putter impacts the golf ball. Barr compensates for angular rotation of the putter by designing the driving face as a convex horizontal curve approximating an ellipse, possibly with a convex vertical curve approximating a second ellipse. However, such a design is believed to be relatively complex and therefore difficult to construct and utilize.
U.S. Pat. No. 4,121,833 to Prueter is also directed to a golf putter which utilizes a curved driving face in an attempt to enhance directional accuracy in spite of inadvertent twisting of the face of the putter during the stroking operation. Preuter's striking surface has the general configuration of a cylindrical segment of substantially constant radius. However, in Preuter, the radius of curvature from the axis of the shaft engaging zone to the striking surface is very small, namely between 21/2 and 41/2 inches. However, such a short radius of curvature significantly increases the chance of error if the putter is moved in a line other than the correct line to the target.
Thus, the need exists to provide an improved putter, which utilizes the concept of a curved driving face, which more effectively compensates for golfer error and thereby enhances the accuracy of the putting stroke.